1. Field
The present application relates generally to the operation and design of amplifiers, and more particularly, to a system providing switchable impedance transformer matching for amplifiers, for example, power amplifiers.
2. Background
Efficient signal amplification is especially important during transmissions from portable devices. Typically, such devices comprise a power amplifier having its output power determined by an optimum impedance on the load line provided by either lumped circuit matching or a transformer that couples the amplifier output to an output transmission path. This configuration results in good efficiency at high output power levels but not at low output power levels.
To illustrate this problem, consider a portable mobile station transmitting data to a base station in a cellular communication system. When the base station is far away, the mobile station increases its transmission power to assure proper communication with the base station. At high output power levels the mobile station's amplifier is operating very efficiently based on the single fixed impedance that couples the amplifier output to the output transmission path. However, as the mobile stations moves closer to the base station, the mobile station may reduce its transmit power. At lower output power levels, the mobile station's amplifier operates less efficiently because the single fixed impedance that couples the amplifier output to the output transmission path provides less efficiency at lower power levels. This reduced efficiency means increased power consumption, which can be very problematic for battery operated portable devices.
Portable devices having multiple communication interfaces present additional problems with respect to signal amplification. For example, a portable device having both wireless LAN (WLAN) and Bluetooth (BT) communication interfaces typically utilizes a separate amplifier for each interface. Not only does this require additional circuitry, but coupling multiple amplifiers into the transmission path may require special switches or other circuitry that may introduce signal loss.
Therefore, it would be desirable to have an amplifier that provides efficient operation at both low and high power levels, and which can be configured to provide amplification for multiple communication interfaces thereby conserving power, circuitry, and maintaining signal quality.